With the recent development of computer aided construction, there has been more and more demand for, for example, precise detection of the position of a work tool of a construction machine in operation, i.e., a work tool that is attached in a rotatable manner to a tip of an arm of a hydraulic shovel. The position of the work tool of a hydraulic shovel is detected by, for example, detecting the angle of rotation of the work tool with respect to the arm. In this regard, a known system includes a construction machine that calculates the angle of rotation of a work tool with respect to an arm. In this construction machine, an angle detector for detecting the angle of rotation of a work tool cylinder with respect to the arm is disposed at the base end (the bottom side) of the work tool cylinder positioned away from the work tool. According to this construction machine, the angle of rotation of the work tool with respect to the arm is calculated from the angle detected by the angle detector, and, because the angle detector is positioned away from the work tool, the angle detector is prevented from being damaged through contact with earth and sand during excavation or the like.
[The problem is further described with reference to FIG. 12 and FIG. 13. The] Conventionally, a work tool is positioned at a dump position when the work tool cylinder is the most retracted. On the other hand, the work tool is positioned at an excavation position when the work tool cylinder is the most elongated. [An operation of rotating the work tool cylinder 122 with respect to the arm 110 while the work tool 112 is rotated from the dump position to the excavation position is now described. First, as shown in FIG. 12, the work tool cylinder 122 is rotated from the position shown by the solid line to the position shown by the two-dot chain line, in the direction shown by the arrow X. Then, as shown in FIG. 13, the work tool cylinder 122 is rotated from the position shown by the two-dot chain line (same as the position shown by the two-dot chain line in FIG. 12) to the position shown by the solid line, in the direction shown by the arrow Y. Therefore, while] While the work tool is rotated in one direction from the discharge position to the excavation position, the work tool cylinder not only rotates in one direction but also rotates in the opposite direction thereafter. For this reason, it is difficult to unambiguously calculate the angle of rotation of the work tool with respect to the arm using only the angle of rotation of the work tool cylinder with respect to the arm.
The present invention was contrived in view of the foregoing circumstances, and the main technical object thereof is to provide a working arm device of a construction machine that is capable of not only unambiguously calculating the angle of rotation of a work tool with respect to an arm, but also preventing angle detection means from being damaged when in contact with, for example, earth and sand during excavation or the like.
As a working arm device of a construction machine that achieves the foregoing technical object, the present invention provides a working arm device of a construction machine, which has an arm, a first link that has one end portion coupled in a rotatable manner to a tip of the arm, a second link that has one end portion coupled in a rotatable manner to the other end portion of the first link, and a work tool that is coupled in a rotatable manner to the other end portion of the second link and is coupled in a rotatable manner to the arm so as to be positioned closer to the tip of the arm than the one end portion of the first link is, the first link being located widthwise outward of a side wall of the arm in a width direction, wherein angle detection means for detecting an angle of rotation of the first link with respect to the arm is disposed between an inner surface of the first link and an outer surface of the side wall of the arm.
It is preferred that the angle detection means is configured with a magnet attached to one of the inner surface of the first link and the outer surface of the side wall of the arm, and a magnetic detector attached to the other of the inner surface of the first link and the outer surface of the side wall of the arm. It is also preferred that the arm is provided with a cylindrical link coupling boss extending in the width direction and protruding from the side wall thereof, that a cylindrical link coupling pin is inserted in a rotatable manner into the link coupling boss, that the one end portion of the first link is fixed to the link coupling pin, and that the magnetic detector has an arc-shaped detecting element extending in the shape of an arc along an outer circumferential surface of the link coupling boss, the magnet being positioned between the outer circumferential surface of the link coupling boss and the arc-shaped detecting element. It is also preferred that the magnet is fixed to the inner surface of the first link, that the magnetic detector is fixed to a cover member, and that the cover member is attached to the outer surface of the side wall of the arm. It is preferred that the cover member is configured with a cover plate that is disposed at a distance from the outer surface of the side wall of the arm in the width direction, and that the magnetic detector is fixed to an inner surface of the cover plate. It is preferred that a through-hole is formed in the cover plate, that an inner circumferential rim of the through-hole has an arc-shaped inner circumferential rim extending in the shape of an arc along the arc-shaped detecting element of the magnetic detector, and that, with the magnetic detector being fixed to the inner surface of the cover plate, the arc-shaped detecting element of the magnetic detector projects toward the inside of the through-hole beyond the arc-shaped inner circumferential rim. The cover plate is preferably provided with a rib protruding widthwise inward from an outer circumferential rim of the cover plate and extending along the outer circumferential rim. It is preferred that the inner surface of the first link is provided with a pair of projections projecting widthwise inward, and that the magnet is positioned between the pair of projections in a circumferential direction of the link coupling pin. It is also preferred that the inner surface of the first link is provided with an annular ridge projecting widthwise inward, that a radial center of the annular ridge is positioned on a central axis line of the link coupling pin, and that the magnet is embedded in the annular ridge.